Study On The Migration Law And Thermodynamic Model Prediction Of Four Kinds Of Antioxidants In Polypropylene

Abstract:Plastics are widely used in food packaging due to their superior properties.In the actual production process,the corresponding small molecule chemical additives are usually added to optimize the quality and performance of the plastic.When plastic packaging directly encloses food,small-molecule additives in plastics migrate are getting into the foods as conditions change.After the food is contaminated,small-molecule additives may accumulate in the body and cause damage to the body after eating.Therefore,the study which the law of the migration about harmful substances into food can effectively reduce the food contamination risk of food packaging materials,provide a theoretical basis for the prediction of migration during plastic production and processing,and thus contain the food pollution problems caused by the migration at the source.The research object of this paper is four kinds of antioxidant BHT,BHA,Irgafos168,Irganox1076 in polypropylene?PP?plastic masterbatch.Under different particle size conditions,n-hexane,cyclohexane,ethyl acetate,n-propanol,iso Butanol and ethanol were used as food simulants.15°C,25°C,35°C and 45°C were selected as the test temperature.High-performance liquid chromatography was used to study the migration of antioxidants in polypropylene?PP?.At the same time,a mathematical model based on the thermodynamics theory of Scatcthard-Hildebrand was established to predict the partition coefficient of the migration about small molecules when the difference between the compatibility of antioxidants and polypropylene and food simulant was used to compare the theoretical model data with experimental data degree.By discussing the effects of temperature,species of migration,particle size of the polymer,and the type of the simulated solution on the difference between them,a further theoretical analysis was performed to measure the applicability of the theoretical model.The main research results are as follows:?1?Four different molecular weight and polarity antioxidants,BHA,BHT,1076 and168,migrated from polypropylene to various simulated liquids.Their antioxidant concentration?Ct?and soaking time?t?were both in accordance with C_t=A(1-e^?-Bt?),and equation has a correlation coefficient R²greater than 98%.?2?The larger the specific surface area of plastic,the greater the migration and migration speed.Only when the plastic particles are infinitesimally small and the specific surface area is infinite,the migration amount can reach the maximum.?3?As the temperature rises,the migration and initial migration velocity?AB value?of the four antioxidants increases,and the rate of increase increases faster,demonstrating that the temperature is higher,the effect on these four antioxidants is bigger.?4?Both the migration and distribution ratio and the initial velocity of migration agree with the lnD_r?V₀?=A+Be^-m/sequation,and the correlation coefficient R²is 0.98.The parameters of each equation are related to the solubility parameters of the simulated solution and the molecular size of the antioxidant.?5?In addition to the influence of migration resistance,the equilibrium migration and distribution ratio is mainly influenced by plastics,antioxidants and simulated liquids.When the solubility parameters of antioxidants and plastics differ greatly,and the solubility parameters of the simulated liquids differ slightly,the larger the migration,the smaller the migration.When the solubility parameters of plastics and simulated liquids differ greatly,the size of the migrating molecules also has a certain influence on the migration.When the solubility parameters of the plastic and the simulated liquid are close to each other,the effect of the molecular size of the migration on the migration is greatly reduced.?6?The experimental value about the equilibrium distribution ratio of the four antioxidants transferred from polypropylene plastics to the solubility parameters within the range of 7.3-13.5,the variation of the solubility parameters of each simulated liquid and the variation of calculated values of Scatchard-Hilderbrand thermodynamics theory are exactly the same,although the experimental value is not equal to the theoretical calculation value due to the influence of the transfer resistance,the value of the infinite specific surface area derived from the experimental value of the simulated liquid n-hexane and also very close to the calculated value of the Scatchard-Hilderbrand thermodynamic theory.Simultaneously increasing the migration temperature also makes the experimental value of the migration close to or equal to the theoretical calculation value.